Enzymatically Cleavable Self-Assembled Nanoparticles for Morphogen Delivery

ABSTRACT

The present disclosure is directed to hybrid multifunctional macromers that can self-assemble to form nanoparticles for on-demand and targeted release of morphogens. Embodiments of the disclosure can include the hybrid multifunctional macromers and peptide sequences incorporated therein, self-assembled nanoparticles including the hybrid multifunctional macromers, methods for producing the hybrid multifunctional macromers and peptide sequences, and methods for treating a disease by the on-demand and targeted delivery of a compound using the hybrid multifunctional macromers.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to provisional application No. 62/847,024, filed May 13, 2019, the entirety of which is incorporated herein by reference.

STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED RESEARCH

This invention was made with Government support under Contract Nos. CBET1403545 and IIP150024, awarded by the National Science Foundation (NSF), and Contract No. AR063745, awarded by the National Institute of Arthritis and Musculoskeletal and Skin Diseases of the National institutes of Health (NIH). The Government has certain rights in the invention.

BACKGROUND

There is a continuing need to develop approaches for controlled release of morphogens in applications such as tissue regeneration. While metal and ceramic particles have been used as delivery systems, these materials can have drawbacks because even though they are biocompatible, there is risk for accumulation in the body, something that may be a particular issue when the site of delivery is already damaged by an injury. Needed in the art are alternative delivery systems that can be functionalized in various ways to both target and trigger release of a compound without leading to bioaccumulation.

In particular, enzyme responsive delivery systems have yet to be developed that take advantage of the secretion of enzymes such as proteases by mesenchymal stem cells (MSCs) and endothelial colony forming cells (ECFCs). Both of these cells express proteases to degrade the extracellular matrix (ECM) as they migrate to sites of injury. MSCs invade the ECM during angiogenesis via different protease families including the plasmin axis of serine proteases and the plasmin-independent matrix metalloproteinases (MMPs). Human MSCs have a strong fibrinolytic activity by expressing key elements of the fibrinolytic cascade including urokinase plasminogen activator (uPA) and its receptor (uPAR), tissue plasminogen activator (tPA) and plasminogen inhibitor PAI. Further, it has been shown that the expression level of fibrinolytic enzymes tPA and uPA in hMSCs is dependent on factors that mediate vascularization and bone formation like basic fibroblast growth factor (bFGF), transforming growth factor-β (TGF-β) and interleukin-1β (IL-1β). Studies on fibrinolytic capacity of MSCs in a fibrin clot indicate that the activity of plasmin and the extent of fibrin degradation during wound healing is controlled by MSCs. By developing nanoparticles that can target and trigger release of a compound at sites of injury without bioaccumulation, difficult applications in tissue engineering can by addressed such as the reconstruction of skeletal defects.

SUMMARY OF THE INVENTION

The present disclosure is directed to hybrid multifunctional macromers that can self-assemble to form nanoparticles for on-demand and targeted release of morphogens. Embodiments of the disclosure can include the hybrid multifunctional macromers and peptide sequences incorporated therein, self-assembled nanoparticles including the hybrid multifunctional macromers, methods for producing the hybrid multifunctional macromers and peptide sequences, and methods for treating a disease by the on-demand and targeted delivery of a compound using the hybrid multifunctional macromers.

Embodiments of the disclosure can provide improved biocompatibility compared to inorganic delivery vehicles while demonstrating therapeutically efficacious treatments for applications such as promoting vascularized osteogenesis. Other features and aspects of the present invention are set forth in greater detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including the best mode thereof to one skilled in the art, is set forth more particularly in the remainder of the specification, which includes reference to the accompanying figures.

FIG. 1 illustrates an example process for forming a nanoparticle from a hybrid multifunctional macromer in accordance with exemplary embodiments of the disclosure.

FIG. 2 illustrates an example system for use with exemplary embodiments of the disclosure.

FIGS. 3A-3F illustrate bar graphs comparing different conditions in accordance with exemplary embodiments of the disclosure.

FIGS. 4A-4E illustrate line graphs showing intracellular (4B and 4D) or extracellular (4A, 4C, and 4E) release of a protein in accordance with exemplary embodiments of the disclosure.

FIGS. 5A-5D illustrate images and histograms displaying particle size of nanoparticles formed from a hybrid multifunctional macromer in accordance with exemplary embodiments of the disclosure.

FIGS. 6A-6D illustrate graphs displaying characteristics (respectively: hydrodynamic size, PDI, ellipticity, and cell viability) of nanoparticles formed in accordance with the disclosure.

FIGS. 7A-7C illustrate line graphs displaying the cumulative release of an example protein after an incubation time in accordance with exemplary embodiments of the disclosure.

FIGS. 8A-8I illustrate graphs displaying DNA content (8A-8C), RUNX2 fold expression (8D-8F), and ALP fold expression (8G-8H) versus incubation time in accordance with exemplary embodiments of the disclosure.

FIGS. 9A-9F illustrate graphs displaying aspects of exemplary embodiments in accordance with the disclosure.

FIG. 10 illustrates stained images taken of channels of a cellular construct under the conditions shown. The top images provide a view of a cross section of the channel. The bottom images provide a view of the length of the channel.

FIGS. 11A-11F illustrate graphs displaying aspects of exemplary embodiments in accordance with the disclosure.

FIG. 11G illustrates a western blot stained for a protein (CD31 or β-Actin) under the condition shown in accordance with embodiments of the disclosure.

FIG. 12 illustrates stained images around an example channel of the cellular construct. The top images provide a view of a cross section of the channel. The bottom images provide a view of the length of the channel.

Repeat use of reference characters in the present specification and drawings is intended to represent the same or analogous features or elements of the present invention.

DETAILED DESCRIPTION

Reference now will be made to the embodiments of the invention, one or more examples of which are set forth below. Each example is provided by way of an explanation of the invention, not as a limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as one embodiment can be used on another embodiment to yield still a further embodiment. Thus, it is intended that the present invention cover such modifications and variations as come within the scope of the appended claims and their equivalents. It is to be understood by one of ordinary skill in the art that the present discussion is a description of exemplary embodiments only and is not intended as limiting the broader aspects of the present invention, which broader aspects are embodied exemplary constructions.

Generally speaking, the present invention is directed to hybrid multifunctional macromers that can self-assemble to form nanoparticles for on-demand and targeted release of morphogens. Embodiments of the disclosure can include the hybrid multifunctional macromers and peptide sequences incorporated therein, self-assembled nanoparticles including the hybrid multifunctional macromers and peptide sequences, methods for producing hybrid multifunctional macromers and peptide sequences, and methods for treating a disease by the on-demand and targeted delivery of a compound.

An example embodiment of the disclosure can include a hybrid multifunctional macromer. The hybrid multifunctional macromer formed in accordance with the disclosure includes a cleavage site, an assembly site, and a solubility region. In general, the cleavage site includes a first amino acid sequence that can be cleaved by a protein; the assembly site includes a second amino acid sequence that can organize through a non-covalent interaction (e.g., pi-pi stacking) to produce a higher order structure; and the solubility region includes a water-soluble polymer. Each of the cleavage site, the assembly site, and the solubility region are linked to one another by one or more covalent bonds to form an exemplary hybrid multifunctional macromer.

In some embodiments, the hybrid multifunctional macromer can include more than one cleavage site. For these embodiments, each cleavage site can have the same or different first amino acid sequences. As an example implementation, the first amino acid sequence can include lysine-phenylalanine-tyrosine-lysine (KFTK), which can be cleaved by plasmin to break one or more of the bonds linking the residues of the first amino acid sequence. As another example implementation, the first amino acid sequence can include the sequence QPQGLAK that is cleaved by MMP-13 enzyme. Though not intended to limit the scope of first amino acid sequences that can be included in the cleavage site, any MMP-/plasmin-cleavable sequence as known in the art can be included in the first amino acid sequence.

In some embodiments, the hybrid multifunctional macromer can include more than one assembly site. For these embodiments, each assembly site can have the same or different second amino acid sequences. As an example implementation, the second amino acid sequence can include at least one phenylalanine (F), such as 2-8 phenylalanine residues (F . . . F.) Additionally, in certain implementations, the phenylalanine residues can be sequentially linked such that each phenylalanine is directly linked to the next phenylalanine (e.g., FFF, FFFF, and FFFFFFFF) without any other amino acids or linkers between each phenylalanine residue. As another example implementation, the second amino acid sequence can include the sequence VVVVVVKK that assembles into vesicles or other sequences that naturally assemble into nanostructures.

Another aspect of the cleavage site, the assembly site, or both sites includes a residue number describing the number of amino acid residues present in the site. For example, the residue number for the amino acid sequence KFTK is 4 since it includes 4 amino acids. As another example, the residue number for the amino acid sequence FFF is 3. Thus, an example hybrid multifunctional macromer in accordance with the disclosure can include at least one cleavage site having a first amino acid sequence that includes at least 4 amino acids. The at least 4 amino acids can include any of combination of the 20 canonical amino acids that can be cleaved by a protein.

In some embodiments, the hybrid multifunctional macromer can include more than one solubility region. For these embodiments, each solubility region can include the same or different water-soluble polymer. As an example implementation, the water-soluble polymer can include polyethylene glycol (PEG.) An aspect of polymers is the ability to adjust the molecular weight of the polymer by altering the degree of polymerization. In some embodiments, the water-soluble polymer can include PEG having a molecular weight between about 1.5 kDa to about 5 kDa; for example, about 1.3 kDa to about 7 kDa or about 1.2 kDa to about 9 kDa. As another example implementation, the water-soluble polymer can include poly(vinyl alcohol) (PVA), copolymers of PEG and PVA, polyvinylpyrrolidone (PVP), copolymers of PEG and PVP, copolymers of PVA and PVP, or terpolymers of PEG, PVA and PVP, or other water-soluble polymers as known in the art.

In embodiments of the disclosure, the hybrid multifunctional macromer can further include one or more linkers. For these embodiments, the linkers may be used to covalently link the cleavage site, the assembly site, and/or the solubility region to one another. For example, an embodiment of the disclosure can include a hybrid multifunctional macromer having a linker (e.g., succinimide) covalently linking an amino acid residue from the cleavage site to the solubility region. As another example embodiment, a hybrid multifunctional macromer of the disclosure can include at least two linkers to covalently link an amino acid residue from a first cleavage site to the solubility region, and to covalently link an amino acid residue from a second cleavage site to the solubility region. In an example implementation, the amino acid residue from the cleavage site can include a cysteine which, upon reaction with maleimide, forms a covalent bond by addition to the thiol group to maleimide ring double bond producing a succinimide linker.

As an example implementation, the linker can include succinimide. In some implementations, the succinimide can be functionalized at the nitrogen (N) bridge to include a hydroxyl (—OH) or propanamide (—CH₂CH₂CONH₂) substitution.

In some embodiments, the hybrid multifunctional macromer can also include an endcap. In an example implementation, the endcap may include a molecule, protein, or other compound linked to the C-terminus and/or N-terminus of an oligopeptide sequence included in the hybrid multifunctional macromer. The endcap can also include a modification such as C-terminus amidation, N-terminus acetylation, or addition of a protecting group.

For embodiments of the disclosure, the hybrid multifunctional macromer can include a sequence order which defines, in part, the connectivity between one or more of the cleavage site, the assembly site, and the solubility region. An aspect of the sequence order can include one or more regions. Each region can include a cleavage site, an assembly site, and/or a solubility region. For hybrid multifunctional macromers that include more than one region, such that both regions include a cleavage site, an assembly site, or a solubility region, the regions are not constrained to require the same cleavage site, assembly site, or solubility region. Example hybrid multifunctional macromers according to the disclosure may include two regions, each region including a cleavage site and an assembly site. In some implementations, the assembly site for each region can be the same (e.g., FFF). In certain implementations, the assembly site for each region can be different (e.g., the first region includes FFF and the second region includes FFFFFFFF).

Additionally, or alternatively, to define the amino acid sequences in each region, the sequence order can be used to define connectivity between regions. For example, a hybrid multifunctional macromer can include a first region including a cleavage site and an assembly site, a second region including a solubility region, and a third region including a cleavage site and an assembly site. The connectivity may include the first region covalently linked to the second region and the second region covalently linked to the third region. In some implementations, regions can be linked at either the C-terminus or N-terminus, which is referred to as backbone-linked since these regions are attached by the backbone of the multifunctional macromer. In certain implementations, the different regions can be linked by a side group of a peptide included in the region. Generally, linkage of one region to a second region does not require that the regions are backbone-linked, and any amino acid, monomer, or linker in the region may be used to form a covalent bond.

Another aspect of the hybrid multifunctional macromer disclosed herein can include a backbone sequence, the backbone sequence including a linear sequence of amino acids which contains the cleavage site. In some implementations, the backbone sequence can include a number of amino acid residues between 6 to 24, such as 8-18, or 9-14. Further, in some embodiments, the multifunctional peptide sequence can include the assembly site linked to a side group of a residue in the backbone sequence, rather than linked to the N-terminus or C-terminus. As an example, the assembly site may be linked to a side chain of an amino acid residue (e.g., lysine, aspartic acid, and glutamic acid). By linking the assembly site to a side chain in the backbone sequence, certain embodiments can include non-linear hybrid multifunctional macromers where the assembly site is not linked to the macromer backbone.

For embodiments having the assembly site linked to a side group of a residue, the assembly site can include a terminus modification. For example, extending a peptide chain from the nitrogen of lysine can result in a free amino group that may be modified (e.g., acetylated) to prevent ionization. As another example, extending a peptide chain from the carboxylate of aspartic acid can result in a free carboxylate group that may be modified (e.g., amidated) to prevent ionization. Thus, in some example embodiments, the assembly site can include a terminus modification such as an N-acetylated residue or a C-amidated residue.

An example embodiment of the disclosure can also include a method for forming a hybrid multifunctional peptide sequence, the method including: synthesizing a backbone amino acid sequence by linking 4-26 amino acids, the backbone amino acid sequence comprising a cleavage site; synthesizing an assembly peptide by linking an assembly site to an amino acid side chain included in the hybrid multifunctional backbone sequence; and attaching a solubility region to the hybrid multifunctional macromer. Generally, for embodiments of the disclosure, the order of synthesis does not matter, and each of the cleavage site, the assembly site, and the solubility region may be linked to one another in any order.

In some implementations, synthesizing the backbone amino acid sequence may be conducted chemically (e.g., by solid phase synthesis) to chemically attach the residues in the backbone sequences. In certain implementations, the backbone amino acid sequence or a substantial portion of the backbone amino acid sequence may be produced using an organism by providing a vector encoding the amino acid sequence to the organism.

In an example embodiment, the method for forming a hybrid multifunctional macromer can include synthesizing a backbone amino acid sequence by linking 12 amino acids to form the sequence GGKFTKGGKGGC (SEQ. ID No: 1) which comprises the cleavage site KFTK. An assembly site can be linked to the backbone amino acid sequence by attaching one or more phenylalanine residues to a lysine in the example sequence. For instance, the 9^(th) residue (K9) of SEQ. ID No: 1 can be linked to an assembly site containing at least one phenylalanine (e.g., GFFF) to form an assembly peptide. To produce the example hybrid multifunctional macromer, a solubility region can be attached to the multifunctional sequence already containing the cleavage site and an assembly site. In an example implementation, the solubility region can be attached to the multifunctional sequence by linking the solubility region to a residue of the backbone sequence. For instance, the 12^(th) residue (C12) of SEQ. ID No: 1 can be linked to the solubility region.

In some example methods for forming a hybrid multifunctional macromer as disclosed herein, the methods may also include attaching a linker, a spacer, or an endcap to the backbone sequence or the assembly site.

An embodiment of the disclosure can also include a method for delivering a compound (e.g., a protein such as bone morphogenic protein or BMP) to a patient in need thereof by administering a nanoparticle composed substantially from hybrid multifunctional macromer as disclosed herein. In general, the nanoparticle composed substantially from the hybrid multifunctional macromer, can include mainly the hybrid multifunctional macromer (e.g., 99% or greater purity by weight). While solvents or ions may be associated with the nanoparticles, these do not affect the purity of the nanoparticles. In an example implementation, the nanoparticle can include a group (e.g., greater than 1) of hybrid multifunctional macromers, where at least one macromer includes an endcap containing the compound. Upon cleavage by a protein, a portion of the macromer including the compound can be released to provide targeted delivery of the compound.

In an embodiment of the disclosure, the method for delivering a compound to a patient can include using an administration route. For example, the administration route can include one or more of the following: intravenous injection, intramuscular injection, oral capsule, sublingual tablet, skin ointment, or anal suppository.

EXAMPLE 1

Example 1 discusses various methods and procedures and provides exemplary embodiments that may be understood in conjunction with the Drawings and Description provided herein. The specific methods and procedures described in Example 1 are not meant to limit the disclosure and are provided solely to illustrate some of the ways in which the invention may be practiced.

Methods

Materials: Actide (L) monomer with >99.5% purity (Ortec, Easley, S.C.) was dried. PEG with molecular weights (MW) of 2.0, 5.0 and 7.5 kDa, PEGDA with 575 Da MW, porcine skin gelatin (type A, 300 bloom), tin (II) 2-ethylhexanoate (TOC), dimethyl sulfoxide (DMSO), methacrylic anhydride (MA), Alizarin red, and 4,6 diamidino-2-phenylindole (DAPI) were received from Sigma-Aldrich (St. Louis, Mo.). Dichloromethane (DCM, Acros Organics, Pittsburg, Pa.) was dried by distillation over calcium hydride. Diethyl ether, dimethylformamide (DMF) and hexane were received from VWR (Bristol, Conn.) and used as received. Dialysis tubing with 0.1-0.5 kDa and 3.5 kDa cutoff MW was received from Spectrum Laboratories (Rancho Dominguez, Calif.). N,N′-disuccinimidyl carbonate (DSC) and bovine serum albumin (BSA) were received from Novabiochem® (San Diego, Calif.) and Jackson ImmunoResearch (West Grove, Pa.), respectively. EBM™2 medium, EGM™-2 BulletKit™ medium, human basic fibroblast growth factor (bFGF), R3-insulin like growth factor-1 (IGF-1), human epidermal growth factor (EGF), ascorbic acid (AA), β-sodium glycerophosphate (βGP), dexamethasone (DEX), hydrocortisone, gentamycin sulfate (GS), penicillin (PN), streptomycin (SP), and amphotericin-B were received from Lonza (Hopkinton, Mass.). PECAM-1 (CD31) and bovine anti-rabbit IgG-FITC (secondary antibody) were received from Santa Cruz Biotechnology (Dallas, Tex.). Human VEGF, rhBMP-2 (hereafter referred to as BMP2), their Enzyme-Linked Immunosorbent Assay (ELISA) kits, and bFGF (FGF2) ELISA kit were received from MyBioSource (San Diego, Calif.). Human plasminogen and MMP-2 ELISA kits were received form Innovative Research (Court Novi, Mich.) and Boster (Pleasanton, Calif.), respectively. Acetomethoxy derivative of calcein (cAM) and ethidium homodimer (EthD) were received from Life Technologies™ (Grand Island, N.Y.), and MTS cell viability assay was received from ThermoFisher (Waltham, Mass.). Quant-iT™ PicoGreen™ dsDNA reagent kit was received from Invitrogen™ (Carlsbad, Calif.). The kits for QuantiChrom™ calcium and alkaline phosphatase (ALP) assays were received from BioAssay Systems (Hayward, Calif.).

Material Synthesis: A two-step procedure was used to synthesize linear LPELA macromonomer. Acrylamide-terminated glycine-arginine-glycine-aspartic acid (Ac-GRGD) cell-adhesive peptide was synthesized and purified. GelMA was synthesized by the reaction of gelatin with methacrylic anhydride. PEG with PEG MW of 12 kDa was chain-extended with short lactide (L) and glycolide (G) blocks (LG/PEG molar ratio of 24 and L:G ratio of 60:40); the chain-ends were terminated with succinimide groups; the macromers were assembled into NGs by dialysis; and VEGF was grafted to the NGs to generate VEGF-NGs. The grafting efficiency of VEGF to the NGs was 92±1%. VEGF was released steadily from VEGF-NGs in 7 days, measured by ELISA.

Synthesis of Plasmin Cleavable NPs: The following approach was used to synthesize the PEG-SPCP conjugate as illustrated in FIGS. 1A-1E. FIGS. 1A-1E illustrate a schematic diagram for the synthesis of a plasmin-cleavable, self-assembled, BMP2-grafted PxSPCP NP. The sequence cysteine-glycine-glycine-lysine with doubly-protected lysine residue [CGGK(α-Fmoc)(ϵ-MTT)] was synthesized in the solid phase on Wang resin. The acetyl-terminated triphenylalanine with a glycine spacer (GFFF-ac) was synthesized separately in the solid phase on Wang resin and coupled to the MTT terminus of CGGK to yield the CGGK(GFFF-ac)(α-Fmoc) sequence. After MTT deprotection, the sequence plasmin-cleavable KFKT with two glycine spacers on each side (GGKFKTGG) was coupled by EDC chemistry to the Fmoc terminus of CGGK(GFFF-ac)(α-Fmoc) to yield the CGGK(GFFF-ac)GGKFKTGG peptide (SPCP) (FIG. 1A). After cleaving from the resin, the SPCP peptide was purified by high-performance liquid chromatography (HPLC) and characterized by electrospray ionization spectrometry. The peptide CGGK(GFFF-ac)GGG without the KFKT sequence (SP) was synthesized to produce NPs that did not undergo cleavage in response to plasmin.

PEG with MW of 2, 5, and 7 kDa was reacted with acryloyl chloride to produce PEGDA. Next, PEGDA in PBS was added dropwise to the solution of SPCP peptide (PEGDA:SPCP molar ratio of 1:2.5) in acetonitrile/PBS (pH 7.4, 1 mM TCEP) in a reaction flask with stirring and nitrogen flow. The reaction between the cysteine groups of SPCP and acrylate groups of PEGDA was allowed to proceed for 6 hours under ambient condition. After the reaction, the PEG-SPCP conjugate was purified by dialysis (500 Da MW cutoff membrane) against PBS and lyophilized (FIG. 1B). Then, the carboxyl end-groups of PEG-SPCP conjugate were succinimide-functionalized by reaction with DSC (FIG. 1C). The chemical structure of the lyophilized PEG-SPCP conjugate was characterized by ¹H-NMR (Varian Mercury-300, Palo Alto, Calif.) and FTIR (PerkinElmer Spectrum™ 100, Waltham, Mass.) The functionalized conjugates with and without the plasmin-cleavable peptide are hereafter referred to as PxSPCP and PxSP, respectively, where the letter “x” is the PEG MW in kDa, “SP” is for the self-assembled peptide FFF, and “CP” is for the plasmin-cleavable peptide KFKT.

To form NPs, the functionalized PxSPCP conjugates were dissolved in DMSO and self-assembled by dialysis against PBS. The NP suspension was freeze-dried to produce a free-flowing powder (FIG. 1D). The average particle size, size distribution, and zeta potential of PxSPCP NPs were measured with a Zetasizer Nano ZS dynamic light scattering (Malvern Instruments, Malvern, UK) at 25° C. in Nano-pure water (Millipore, Billerica, Mass.) To observe particle shape, 20 μL of the suspension was deposited onto a 300-mesh carbon-coated copper grid and imaged with a transmission electron microscope (Hitachi H8000, Schaumburg, Ill.).

Cell Culture: Human MSCs (Lonza, Allendale, N.J.) were cultured in basal MSC medium (high-glucose DMEM supplemented with 10% FBS, 100 units/mL penicillin and 100 μg/mL streptomycin) at a seeding density of 5000 cells/cm². Human ECFCs (Boston Children's Hospital) were cultured on 1% gelatin coated flasks in basal ECFC medium (BulletKit™ EBM™-2 medium supplemented with 20% FBS) at a density of 6500 cells/cm².

Cell Encapsulation in LPELA and GelMA Hydrogels: The LPELA precursor solution was prepared by mixing 200 mg LPELA, 4 mg Ac-GRGD cell-adhesive peptide (2% by weight of LPELA) and 1.5 mg photo-initiator (0.75 wt %) in 1 mL PBS. After sterilization by filtration, hMSCs at a density of 2×106 cells/mL were added to the sterile LPELA solution, the suspension was injected between two sterile glass slides separated by a spacer and crosslinked by UV irradiation. The GelMA precursor solution was prepared by mixing 50 mg GelMA and 0.375 mg photo-initiator (0.75 wt %) in 1 mL PBS. After sterilization by filtration, a 50:50 mixture of hMSCs+ECFCs at a total density of 2×106 cells/mL were added to the sterile GelMA solution, injected between two sterile glass slides separated by a spacer and crosslinked by UV irradiation. After washing with PBS, the cell-encapsulated LEPLA or GelMA hydrogels were cultured in the appropriate medium for osteogenic or vasculogenic differentiation, respectively.

Grafting BMP2 to PxSPCP NPs and Protein Release: BSA was grafted to PxSPCP NPs for particle size analysis, grafting efficiency and protein stability studies whereas BMP2 was grafted for protein release and cell culture experiments. For grafting, 10 mg PxSPCP NPs were dispersed in PBS by sonication for 5 minutes. Next, 0.5 mL of BMP2 (400 ng/mL) or BSA (20 mg/mL) were added to the NP suspension and the grafting reaction between the free amine groups of BMP2 or BSA and the succinimide groups of the NPs was allowed to proceed overnight under ambient condition to produce BMP2-PxSPCP NPs (FIG. 1E). After the reaction, the suspension was centrifuged at 15000 rpm for 10 minutes and the amount of free (not grafted) BMP2 or BSA in the supernatant was quantified by ELISA or BCA protein assay, respectively.

For release studies, plasmin (0.2 U/mL) was added to the suspension of 10 mg BMP2-PxSPCP NPs in 1 mL PBS and incubated at 37° C. with shaking at 50 rpm. At each time point, the suspension was centrifuged at 10,000 rpm for 5 minutes, the supernatant containing the free BMP2 was collected and replaced with fresh plasmin solution. BMP2 content of the supernatant solution was measured with a BMP2 ELISA kit. BMP2 added directly to the plasmin solution and BMP2-PxSP NPs were used as control groups.

Bioactivity and Cell Compatibility of BMP2-PxSPCP NPs: Circular dichroism (CD) was used to determine the effect of grafting on secondary structure of the model BSA protein. CD spectra of free or grafted BSA in PBS were collected with a spectropolarimeter (JASCO J815, Essex, UK) at 20° C. with a cuvette of 0.1 cm path length. For evaluation of cell compatibility, hMSCs (1×106 cells/mL) and PxSPCP NPs (10 mg) were encapsulated in LPELA hydrogel and cultured in basal medium. At each time point, the hydrogels were stained with cAM/EthD live/dead assay (1 μg/mL) and the stained cells were imaged with an inverted fluorescent microscope (Nikon Eclipse Ti-ϵ, Nikon, Melville, N.Y.) To quantify cell viability, the medium was replaced with fresh medium containing 10% MTS and incubated for 6 hours at 37° C. and the sample absorbance was measured with a microplate reader (Molecular Devices, San Jose, Calif.) at a wavelength of 490 nm.

The bioactivity of BMP2 released from the NPs was determined by measuring the expression of osteogenic markers for hMSCs encapsulated in LPELA hydrogel and incubated in the osteogenic medium (without BMP2 or DEX) supplemented with BMP2 released from the NPs. The measured markers of osteogenic differentiation included RUNX2 (early marker) and calcium (late marker). Control groups included hMSCs encapsulated in LPELA hydrogel and incubated in osteogenic medium with or without BMP2 directly added to the medium.

Measurement of Protease Expression of Encapsulated hMSCs and ECFCs: hMSCs at a density of 2×106 cells/mL were encapsulated in LPELA hydrogel, whereas ECFCs or a 50:50 mixture of hMSCs+ECFCs at a total density of 2×106 cells/mL were encapsulated in GelMA hydrogel as described. After gelation, disk-shape samples were cut from the gels and incubated in the appropriate medium for up to 7 days. hMSCs encapsulated in LPELA were cultured in osteogenic medium, whereas ECFCs or hMSCs+ECFCs in GelMA were cultured in vasculogenic medium. At each time point, samples were divided into two parts for analysis. One part was used for measurement of differential RNA expression of plasminogen, uPA, tPA, matrix metalloproteinase-2 (MMP-2), and membrane-type matrix metalloproteinase-1 (MT-MMP-1) by real-time polymerase chain reaction (RT-qPCR.) The gene specific primers for RT-qPCR were designed and selected using the Primer3 web-based software. The forward and reverse primers, synthesized by Integrated DNA Technologies™ (Coralville, Iowa), are listed in Table 1. The expression of GAPDH house-keeping gene was used as a reference and the model of Pfaffl was used to determine the expression ratio of the genes. The other part was used to quantify protein expression of the total plasmin and MMP-2 in the intracellular and extracellular compartments as well as the extracellular expression of bFGF. To quantify the extracellular expressions, the medium of the hydrogel cultures was centrifuged at 15000 rpm for 10 minutes to separate the insoluble residue; the supernatant was concentrated 5-fold using a 10 kDa cutoff membrane; and the protein concentration was measured by ELISA. To quantify the intracellular expressions, the hydrogel sample was washed, digested in RIPA buffer, centrifuged at 15000 rpm for 15 minutes, and the concentration of proteins in the supernatant was measured by ELISA.

Encapsulation of hMSCs and ECFCs in Patterned Constructs: Patterned hydrogel constructs with GelMA micro-channels in LPELA matrix were generated for co-culture experiments (FIG. 2). FIG. 2 displays a schematic diagram for generating the patterned cellular constructs. The LPELA hydrogel precursor solution loaded with hMSCs and BMP2-PxSPCP NPs was injected inside a Teflon® cylinder fitted with needles. After LPELA gelation, needles were removed and the GelMA precursor solution loaded with ECFCs+hMSCs and VEGF-NGs was injected in the microchannels and crosslinked. The constructs were cultured in appropriate medium with time and analyzed with respect to the expression of markers for osteogenesis and vasculogenesis.

Needles with a diameter of 400 μm and inter-needle separation of 500 μm were inserted through the endcaps of a cylindrical Teflon® mold with diameter and height of 5 and 3 mm, respectively (FIG. 2). Next, the sterile LPELA precursor suspension composed of 200 mg LPELA, 4 mg Ac-GRGD cell-adhesive peptide, 1.5 mg photo-initiator, 20 mg plasmin-cleavable PxSPCP NPs, and 2×106 hMSCs in 1 mL PBS was injected in the cylindrical mold and crosslinked by UV irradiation. Then, the needles were removed from the LPELA matrix, and the sterile GelMA precursor suspension composed of 50 mg GelMA, 0.375 mg photo-initiator, 2 mg VEGF-NGs, 2×106 of 50:50 hMSCs+ECFCs was injected in the channels and crosslinked by UV irradiation. After gelation, the patterned hydrogel constructs were washed with warm PBS, cultured in basal medium for one day, followed by cultivation in vasculogenic medium (without VEGF) for days 2-7, 50:50 mixture of vasculogenic and osteogenic medium (without VEGF, BMP2 or DEX) for days 8-10, and finally in osteogenic medium (without DEX or BMP2) for days 11-21.

Biochemical, mRNA and Protein Analysis and Immunofluorescent Staining: At each time point after washing the hydrogel constructs to remove serum proteins and sonicating to lyse the encapsulated cells, 43 samples were divided into four groups for biochemical, mRNA and protein analysis, and immunofluorescent staining. For biochemical analysis, the double-stranded DNA content, ALP activity, and calcium content of the homogenized samples were measured. For mRNA expression, the RNA of the homogenized samples was extracted and used for measurement of mRNA expression of osteogenic markers (RUNX2, Col I, and ALP) and vasculogenic markers (vWF, VEGFR, VE-cadherin, and CD31). To compare expression between the groups, mRNA-fold difference for expression of the gene of interest was normalized to that of GAPDH, followed by normalization against day one expression. The expression of CD31 vasculogenic marker of the homogenized samples at the protein level was quantified by western blot. Alizarin red and immunofluorescent staining were used to image the intensity of mineralization and CD31 expression. The stained samples were imaged with a Nikon Eclipse Ti-ϵ inverted fluorescent microscope.

Statistical Analysis: All experiments were done in triplicate. Significant differences between experimental groups were evaluated using a two-way ANOVA™ with replication test, followed by a two-tailed Student's t test. A value of p<0.05 was considered statistically significant.

Results

Temporal Expression of Proteases by the Encapsulated hMSCs and ECFCs: The mRNA expressions of uPA, tPA, and plasminogen in the fibrinolytic cascade for the LPELA encapsulated MSCs, GelMA encapsulated ECFCs, and GelMA encapsulated MSCs+ECFCs with incubation time are shown in FIGS. 3A, 3B, and 3C, respectively; the mRNA expressions of MMP-2 and MT-MMP-1 for the encapsulated MSCs, ECFCs, and MSCs+ECFCs are shown in FIGS. 3D-3F, respectively. The encapsulated hMSCs expressed significant levels of uPA, tPA, plasminogen, MMP-2, and MT-MMP-1 in osteogenic medium (days 1, 4, and 7) as shown in FIGS. 3A and 3D. The expression of uPA by MSCs did not change with differentiation in osteogenic medium, whereas that of tPA decreased, those of plasminogen and MMP-2 increased, and that of MT-MMP-11 peaked on day 4. The encapsulated ECFCs did not express significant levels of proteases of the fibrinolytic cascade and the expressions did not change with differentiation in vasculogenic medium (FIGS. 3B and 3E). The encapsulated hMSCs+ECFCs expressed significant levels of tPA and plasminogen with differentiation in vasculogenic medium but did not express uPA, MMP-2 and MT-MMP-1. The expression of tPA of hMSCs+ECFCs peaked on day 4, whereas that of plasminogen increased slightly with differentiation in the vasculogenic medium.

Based on mRNA results, the extra- and intra-cellular expressions of plasmin and MMP-2, as well as extracellular expression of bFGF for the encapsulated hMSCs, ECFCs, and hMSCs+ECFCs, were measured at the protein level and the expressions are shown in FIG. 4. FIG. 4 displays extra- and intra-cellular protein expressions for MMP-2 (FIGS. 4A-4B), total plasmin (FIGS. 4C-3D), and the extra-cellular protein expression of bFGF (FIG. 4E) for MSCs (square, 6), ECFCs (diamond, 7), and MSCs+ECFCs (triangle, 8). MSCs were encapsulated in LPELA hydrogel and cultured in osteogenic medium whereas ECFCs and MSCs+ECFCs were encapsulated in GelMA and cultured in vasculogenic medium.

For all cell types, the expressions of plasmin, MMP-2 and bFGF increased with cell differentiation. For all cell types, the extracellular expression of MMP-2 was higher than the intracellular (FIGS. 4A and 4B), whereas the difference was not significant for plasmin (FIGS. 4C and 4D). After 7 days of culture, the extracellular expression of bFGF by the encapsulated hMSCs in osteogenic medium was higher than the ECFCs or hMSCs+ECFCs in vasculogenic medium with hMSCs+ECFCs showing the lowest bFGF expression (FIG. 4E). Based on the results in FIGS. 3A-3F and FIGS. 4A-4E, the encapsulated hMSCs showed higher expression of proteases with differentiation in osteogenic medium as compared to ECFCs or hMSCs+ECFCs in vasculogenic medium. Therefore, BMP2 was conjugated to plasmin-cleavable PxSPCP NPs and co-encapsulated with hMSCs in LPELA hydrogel of the patterned matrix for on-demand release of BMP2 in response to plasmin expression by hMSCs. As plasmin and MMP-2 expression by the encapsulated hMSCs+ECFCs was relatively low, VEGF was conjugated to hydrolytically degradable NGs and co-encapsulated with hMSCs+ECFCs in GelMA hydrogel of the patterned matrix for release in the first 7 days to stimulate vasculogenic differentiation of the encapsulated ECFCs in the channels.

Characterization of PxSPCP macromer: The mass spectra of CGGK(GFFF-ac)GGKFKTGG (SPCP, MW=1638.9 Da) and CGGK(GFFF-ac)GGG (SP, MW=1018.2 Da) polypeptides were determined. In the SPCP spectrum, m/z values of 820 and 1638 Da corresponded to the divalent [(M+2H)]2+ and monovalent [(M+H)]+1 hydrogen cations of the peptide, respectively. In the SP spectrum, m/z value of 1018 Da corresponded to the monovalent [(M+H)]+hydrogen cation of the peptide. The retention times of SPCP and SP peptides were 10.1 minutes and 11.0 minutes, respectively. The ¹H-NMR spectra of PEGDA and PEG-SPCP-NHS (PxSPCP) were also obtained. Two chemical shifts with peak positions at 3.6 and 4.2 ppm in the spectrum of PEGDA were attributed to the methylene hydrogens of PEG attached to ether and ester groups, respectively; three chemical shifts with peak positions between 5.85-6.55 ppm were attributed to vinyl hydrogens of the acrylate groups at chain ends. The disappearance of chemical shifts for methylene protons (5.85-6.55 ppm) of the acrylate groups in the spectrum of PxSPCP confirmed conjugation of the peptide to PEGDA. Further, the appearance of a shift due to methylene hydrogens with peak position at 2.77 ppm confirmed succinimide functionalization of PxSPCP. The FTIR spectra of PEGDA, PEG-SPCP, and PEG-SPCP-NHS were obtained. The appearance of characteristic absorption bands in the spectra of PEG-SPCP and PEG-SPCP-NHS with peak positions at 1630 and 3330 cm⁻¹ due to vibrations of amides and secondary amines, respectively, confirmed the conjugation of peptide to PEGDA. The appearance of a characteristic band with peak position at 1779 cm⁻¹ due to vibrations of NHS group confirmed succinimide functionalization of PEG-SPCP-NHS.

Characterization of PxSPCP NPs: The number-average size distribution of PxSPCP NPs with or without BSA protein grafting for PEG MW of 0.5 kDa, 2 kDa, 5 kDa, and 7.5 kDa are shown in FIGS. 5A-5D, respectively. The corresponding TEM images of the NPs are shown in the inset of FIGS. 5A-5D. The average particle size, polydispersity index (PDI), and zeta potential of PxSPCP NPs as a function of PEG MW are listed in Table 1. The average size of the NPs increased from 145±15 nm to 225±10, 265±20 and 325±25 nm as the PEG MW was increased from 0.5 kDa to 2 kDa, 5 kDa, and 7.5 kDa, respectively. The size distribution of the NPs was relatively narrow and increased with PEG MW. The average size of P0.5SPCP NPs increased slightly after BSA grafting and the size increase with BSA grafting increased with PEG MW.

The effect of incubation time in basal culture medium on the average size and size distribution for different PEG MW of PxSPCP NPs is shown in FIGS. 6A and 6B, respectively. FIGS. 6A-6D display average particle size distribution (6A) and polydispersity index (PDI) (6B) measured by dynamic light scattering (DLS) for P0.5SPCP (diamond), P2SPCP (square), P5SPCP (circle), and P7.5SPCP (triangle) NPs with incubation time. Also shown are CD spectra (6C) of BSA grafted to P0.5SPCP, P2SPCP, P5SPCP, and P7.5SPCP NPs and free BSA. The viability of hMSCs incubated in basal medium (6D) are shown under conditions supplemented with P0.5SPCP (black), P2SPCP (lighter gray), P5SPCP (gray) and P7.5SPCP (light gray) NPs. Error bars correspond to means ±1 SD for n=3.

For P0.5SPCP NPs, the hydrodynamic size increased significantly from 200 nm on day 1 to 500 nm on day 7, and PDI increased from 0.13 on day 1 to 0.38 on day 7, which was attributed to particle aggregation. For P2SPCP NPs, the average size increased slightly from 225 nm on day 1 to 260 nm on day 7, and PDI did not change with incubation time. For P5SPCP and P7.5SPCP NPs, the average size and PDI did not change with incubation time. The results in FIGS. 6A and 6B indicate that P0.5SPCP NPs aggregated in culture medium, whereas P2SPCP, P5SPCP, and P7.5SPCP were relatively stable in culture medium with incubation. The effect of BSA grafting on the CD spectrum of PxSPCP NPs as a function of PEG MW is shown in FIG. 6C. The absorption spectrum of BSA-P0.5SPCP NPs was close to that of free BSA, whereas there was a slight change in absorption spectrum of BSA-P2SPCP NPs in the 200-125 nm region. The CD spectra of BSA-P5SPCP and BSA-P7.5SPCP were substantially different from that of free BSA. Therefore, the conformational stability of the grafted BSA decreased with increasing PEG MW of the NPs. Based on the CD results, P0.5SPCP and P2SPCP maintained the secondary structure of grafted BSA, whereas P5SPCP and P7.5SPCP denatured the grafted protein. The effect of supplementing the culture medium with PxSPCP NPs of different PEG MW on viability of hMSCs is shown in FIG. 6D. The viability of hMSCs decreased slightly with increasing PEG MW after 3 days of incubation in basal medium. However, viability of hMSCs was >90% for all PxSPCP NPs. Since PEG2SPCP NPs had a relatively stable size distribution in culture medium (FIGS. 6A and 6B), only a slight effect on the secondary structure of grafted BSA (FIG. 6C), and negligible toxicity toward hMSCs (FIG. 6D), these NPs were selected for vascularized osteogenesis experiments with hMSCs and ECFCs in the patterned hydrogels.

Release Characteristics and Bioactivity of BMP2-PxSPCP NPs: The grafting efficiency of BMP2 to PxSPCP NPs decreased from 73.1±2.7% to 69.5±3.2% and 24.5±1.4% as the PEG MW was increased from 2 kDa to 5 kDa and 7.5 kDa, respectively. This decrease was attributed to higher entrapment of the reactive succinimide groups of PxSPCP within the NPs' core with increasing PEG MW, which reduced their availability for BMP2 grafting. BMP2-PxSPCP NPs were encapsulated in LPELA hydrogel, the hydrogel was incubated in PBS, and the release of BMP2 to the incubating medium was measured with time by ELISA. FIGS. 7A-7C show the release kinetic of BMP2 from the encapsulated NPs in LPELA hydrogel with PxSPCP PEG MW of 2 kDa (FIG. 7A), 5 kDa (FIG. 7B), and 7.5 kDa (FIG. 7C), respectively. FIG. 7 displays (A) The cumulative release kinetics of BMP2 from BMP2-P2SPCP (square, 9) and BMP2-P2SP NPs (dashed, 10) encapsulated with plasmin in LPELA hydrogel with incubation time; (B) release of BMP2 from BMP2-P5SPCP (square, 13) and BMP2-P2SP NPs (dashed, 14) encapsulated with plasmin in the hydrogel; and (C) release of BMP2 from BMP2-P7.5SPCP (square, 15) and BMP2-P2SP NPs (dashed, 16) encapsulated with plasmin in the hydrogel. The additional lines in (FIGS. 7A-7C) provide the release of free BMP2 with (circle, 11) and without (circle, 12) plasmin from LPELA hydrogel; the + and − signs correspond to with and without plasmin, respectively. Error bars correspond to means ±1 SD for n=3.

Experimental groups included BMP2-PxSPCP NPs plus plasmin encapsulated in the hydrogel (9, 13, 15 in FIGS. 7A-7C, respectively), BMP2-PxSP NPs plus plasmin in the hydrogel (dash 10, dash 14 or dash 16 in FIGS. 7A-7C, respectively), free BMP2 in the hydrogel (11), and free BMP2 plus plasmin in the hydrogel (12). Approximately 80% of the loaded free BMP2 was released from the hydrogel after 21 days of incubation; the addition of plasmin to the hydrogel did not affect BMP2 release. The incomplete (<100%) release of free BMP2 from the hydrogel was attributed to protein adsorption to the matrix or protein denaturation during hydrogel encapsulation and gelation. ELISA measurements detected relatively small but significant BMP2 activity with incubation time for BMP2-PxSP NPs and plasmin encapsulated in the hydrogel (see 10, 14, or 16 in FIGS. 7A-7C), but the activity decreased with increasing PEG MW of the NPs. The cumulative BMP2 activity after 21 days associated with the encapsulated BMP2-PxSP NPs with PEG MW of 2 kDa, 5 kDa, and 7.5 kDa was 30%, 20% and 19% of the total BMP2 loaded in the hydrogel, respectively. This BMP2 activity was attributed to the release of BMP2-PxSP NPs from the hydrogel which was subsequently detected by ELISA. The BMP2 grafted to PxSPCP NPs and co-encapsulated in the hydrogel with plasmin was gradually released to the medium with incubation time at a rate faster than BMP2-PxSP NPs but slower than the free BMP2. For example, the cumulative release of BMP2 from the encapsulated BMP2-P5SPCP NPs was 60% after 21 days which was higher than the encapsulated P5SP NPs at 20% and slower than the free BMP2 at 80%. The results in FIGS. 7A-C demonstrate that BMP2 was cleaved by plasmin from PxSPCP NPs, leading to the gradual release of the protein from the hydrogel.

Osteogenic Activity of BMP2 Released from PxSPCP NPs: BMP2-PxSPCP NPs (PEG MW of 2 kDa, 5 kDa, and 7.5 kDa) and hMSCs were co-encapsulated in LPELA hydrogel, incubated in osteogenic medium without DEX, and the extent of osteogenesis was measured with incubation time. The DNA contents of hMSCs with incubation time for BMP2-PxSPCP NPs with PEG MW of 2 kDa, 5 kDa, and 7.5 kDa are shown in FIGS. 8A-8C, respectively; mRNA expressions of RUNX2 are shown in FIGS. 8D-8F; and ALP mRNA expressions are shown in FIGS. 8G-8I. Experimental groups included BMP2-P2SPCP NPs (17), BMP2-P2SP NPs (18), BMP2-P5SPCP NPs (22), BMP2-P5SPCP NPs (23), BMP2-P7.5SPCP NPs (24), and BMP2-P7.5SP NPs (25) co-encapsulated with hMSCs in LPELA hydrogel. Control groups were hMSCs encapsulated in LPELA hydrogel and incubated in osteogenic medium supplemented with (19) or without (21) BMP2, and hMSCs co-encapsulated with BMP2 in the hydrogel and incubated in osteogenic medium without DEX (20). The DNA content of all groups decreased with incubation time. DNA content of those groups incubated in osteogenic medium without BMP2 or with BMP2-PxSP NPs decreased at a slower rate compared to those with BMP2 or BMP2-PxSPCP NPs, consistent with previous reports.

The expression of RUNX2 initially increased from day 4 to 7 for all experimental groups, peaked on day 7, followed by a decrease from day 7 to 14 for all BMP2-PxSPCP NPs (FIGS. 8D-8F). Osteogenic activity of the experimental groups was measured by peak RUNX2 expression of the encapsulated hMSCs. Osteogenic activity of the group with BMP2 added to the medium was higher than the group with BMP2 co-encapsulated with hMSCs in the hydrogel, which was attributed to denaturation of a small but significant fraction of the encapsulated BMP2 during hydrogel formation. Osteogenic activity of BMP2-PxSP NP groups (dash lines: 18, 23, and 25, respectively, in FIGS. 8D-8F) was similar to that of no BMP2 group (21 in FIGS. 8D-8F), demonstrating that BMP2 grafted to non-cleavable NPs had negligible osteogenic activity. The BMP2-PxSPCP NP groups showed significantly higher osteogenic activity compared to non-cleavable BMP2-PxSP NPs, thus confirming that a significant fraction of BMP2 grafted to BMP2-PxSPCP NPs was cleaved by plasmin secreted by the encapsulated cells. Further, osteogenic activity of BMP2-P2SPCP-NP and BMP2-P5SPCP-NP groups (17 in FIG. 8D and 22 in FIG. 8E) were similar to that of free BMP2 added to the culture medium, whereas that of BM2-P7.5SPCP-NP group (24 in FIG. 8F) was lower. This result was attributed to higher availability of the plasmin-cleavable peptide in P2SPCP and P5SPCP NPs for enzymatic cleavage. The peak RUNX2 expression of hMSCs for BMP2-P2SPCP-NP and BMP2-P5SPCP-NP groups was 5.7, which was significantly higher than BMP2-P7.5SPCP-NP at 4.2.

FIGS. 8A-8I display DNA content (8A-8C) and mRNA expression of osteogenic markers RUNX2 (8D-8F) and ALP (8G-8I) with incubation time for hMSCs co-encapsulated with BMP2-PxSPCP NPs (PEG MW of 2 kDa, 5 kDa, or 7.5 kDa) in LPELA hydrogel and incubated in osteogenic medium (without DEX). FIGS. 8A, 8D and 8G are for DNA content and expressions of RUNX2 and ALP for BMP2-P2SPCP NPs (solid brown), respectively; FIGS. 8B, 8E and 8H are for BMP2-P5SPCP NPs (solid gray); and FIGS. 8C, 8F and 8I are for BMP7.5SPCP NPs (solid blue). Groups included BMP2-P2SPCP NPs (17), BMP2-P2SP NPs (18), BMP2-P5SPCP NPs (22), BMP2-P5SPCP NPs (23), BMP2-P7.5SPCP NPs (24), and BMP2-P7.5SP NPs (25) co-encapsulated with hMSCs in LPELA hydrogel. Control groups were hMSCs encapsulated in LPELA hydrogel and incubated in osteogenic medium supplemented with BMP2 (19) or without BMP2 (21), and hMSCs co-encapsulated with free BMP2 in the hydrogel (green) and incubated in osteogenic medium without BMP2 or DEX (20). Error bars correspond to means ±1 SD for n=3.

ALP mRNA expression of the encapsulated hMSCs peaked on day 14 for all experimental groups (FIGS. 8G-8I). Similar to RUNX2 expressions, the peak ALP expression of the group with BMP2 added to the medium was higher than the group with BMP2 co-encapsulated with hMSCs in the hydrogel; peak ALP expression of BMP2-PxSP NP groups (dash lines: 18, 23, and 25, respectively, in FIGS. 8G-8I) was similar to that of the no BMP2 group (21 in FIGS. 8D-8F); and peak ALP expression of BMP2-PxSPCP NP groups was significantly higher than the non-cleavable BMP2-PxSP NPs. The BMP2-P2SPCP-NP group (17 in FIG. 8G) had the highest peak ALP expression followed by BMP2-P5SPCP (22 in FIG. 8H), with BMP2-P7.5SPCP (24 in FIG. 8I) as the lowest. The peak ALP expression of hMSCs for BMP2-P2SPCP-NP, BMP2-P5SPCP-NP and BMP2-P7.5SPCP-NP groups was 60, 52 and 48, respectively. As P2SPCP NPs had the most stable size distribution (FIGS. 6A-6B), negligible loss of secondary structure of the grafted protein (FIG. 6C), and highest osteogenic activity of the grafted BMP2 (FIGS. 8A-8I), these NPs were selected for co-culture experiments with hMSCs and ECFCs in the patterned hydrogels.

Osteogenic and Vasculogenic Differentiation of hMSCs and ECFCs in Patterned Hydrogels with Plasmin-Cleavable BMP2-P2SPCP NPs: The effect of on-demand release of BMP2 from plasmin-cleavable NPs on osteogenesis and vasculogenesis was investigated in patterned hydrogels consisting of GelMA microchannels encapsulating hMSCs+ECFCs/VEGF-NGs in LPELA matrix encapsulating hMSCs/BMP2-P2SPCP-NPs. The results are shown in FIGS. 9A-9F, FIG. 10, FIGS. 11A-11G, and FIG. 12. All experimental groups were cellular. The groups included patterned constructs with BMP2-P2SPCP-NP in LPELA matrix and VEGF-NG in GelMA channels (BMP2-P2SPCP-NP/VEGF-NG, 27); unpatterned constructs with BMP2-P2SPCP-NP+VEGF-NG in a mixture of LPELA+GelMA with a composition identical to the patterned matrix (BMP2-P2SPCP-NP+VEGF-NG UnP, 26); patterned constructs with BMP2-P2SPCP-NP in LPELA and GelMA channels without VEGF (BMP2-P2SPCP-NP, 28); patterned constructs with LPELA without BMP2 and VEGF in GelMA channels (VEGF-NG, 32, see FIGS. 11A-F); patterned constructs with BMP2 in LPELA and VEGF in GelMA (BMP2/VEGF, 29); patterned constructs without BMP2 or VEGF (None, 30); and unpatterned constructs based on a mixture of LPELA+GelMA with a composition identical to the patterned matrix without BMP2 or VEGF (None UnP, 31).

The DNA content, calcium content, ALP activity, mRNA expression of osteogenic makers RUNX2, ALP, and Col I of the patterned cellular constructs are shown in FIGS. 9A-F. FIGS. 9A-F display DNA content (A), mRNA expression of osteogenic markers RUNX2 (B), ALP (C), Col I (D) and calcium content (E), and ALP activity (F) with incubation time for hMSCs and ECFCs encapsulated in the patterned constructs. Groups included patterned constructs with BMP2-P2SPCP-NP/VEGF-NG (27), patterned with BMP2/VEGF (29), un-patterned with BMP2-P2SPCP-NP/VEGF-NG (26), patterned with NP-P2SPCP-NP (28), patterned without BMP2/VEGF (30), and unpatterned without BMP2/VEGF (31). An asterisk represents a statistically significant difference between the test and “None” groups for the same time point. Two asterisks represent a significant difference between the test group and the patterned BMP2/VEGF group. Error bars correspond to means ±1 SD for n=3.

The DNA content of all BMP2 or BMP2/VEGF groups (FIG. 9A) decreased with incubation time, consistent with previous reports. For all groups, RUNX2 expression (FIG. 9B) of the encapsulated cells peaked on day 14, whereas Col I expression (FIG. 9D) and calcium content (FIG. 9E) steadily increased with incubation time. For the NP groups, ALP activity peaked on day 18 (FIGS. 9C and 9F), whereas it peaked on day 14 for the free BMP2/VEGF group. The groups with BMP2 and VEGF (with or without grafting to NPs/NGs) had the highest peak expression of osteogenic markers RUNX2 and ALP, as well as the highest Col I expression and calcium content on day 21. Among the groups with BMP2 and VEGF, the patterned BMP2-P2SPCP-NP/VEGF-NG group had the highest expression of osteogenic markers followed by the patterned BMP2/VEGF, unpatterned BMP2-P2SPCP-NP+VEGF-NG, and patterned BMP2-P2SPCP-NP groups. For example, the Col I-fold expressions of patterned BMP2-P2SPCP-NP/VEGF-NG, patterned BMP2/VEGF, unpatterned BMP2-P2SPCP-NP+VEGF-NG, and patterned BMP2-P2SPCP-NP groups were 25, 20, 22, and 15, respectively (FIG. 9D); the calcium contents were 770, 695, 665, and 390 mg/mg DNA (FIG. 9E); and ALP activities were 6600, 5000, 4850, and 2550 IU/mg DNA (FIG. 9F). Interestingly, the calcium content, ALP activity, and expression of osteogenic markers for patterned BMP2-P2SPCP-NP group was significantly less than those of BMP2-P2SPCP-NP/VEGF-NG, BMP2/VEGF and unpatterned BMP2-P2SPCP-NP+VEGF-NG groups. This finding can be attributed to the lack of paracrine signaling between hMSCs and ECFCs in the absence of VEGF-NGs. The images for Alizarin red staining of the patterned BMP2-P2SPCP-NP/VEGF-NG, BMP2/VEGF and BMP2-P2SPC-NP groups are shown in FIG. 10. FIG. 10 displays grayscale images of Alizarin red-stained photographs around one of the channels of the cellular constructs for patterned BMP2-P2SPCP-NP/VEGF-NG (left), patterned BMP2/VEGF (center), and patterned BMP2-P2SPCP-NP (right) groups after 21 days of incubation. The top and bottom rows show the stained images in cross-section and along the length of the channel, respectively. The images show robust mineralization and nodule formation for these groups with the patterned BMP2-P2SPCP-NP/VEGF-NG group showing the most intense staining.

The DNA content, mRNA expression of vasculogenic markers vWF, VEGFR and VE-cadherin, and protein expression of CD31 vasculogenic marker of the patterned constructs are shown in FIGS. 11A-11G. FIGS. 11A-11G display DNA content (A), mRNA expression of vasculogenic markers vWF (B), VEGFR (C), VE-cadherin (D), CD31 (E), and CD31 protein expression (F), along with representative western blot bands (G) with incubation time for hMSCs and ECFCs encapsulated in the patterned constructs. Groups included patterned constructs with BMP2-P2SPCP-NP/VEGF-NG (27), patterned with BMP2/VEGF (29), unpatterned with BMP2-P2SPCP-NP/VEGF-NG (28), patterned with VEGF-NG (32), patterned without BMP2/VEGF (30), and unpatterned without BMP2/VEGF (31). An asterisk represents a statistically significant difference between the test and “None” groups for the same time point. Two asterisks represent a significant difference between the test group and the patterned VEGF/BMP2 group. Error bars correspond to means ±1 SD for n=3.

DNA content of the groups with BMP2/VEGF or VEGF only decreased with incubation time with differentiation of the encapsulated hMSCs and ECFCs. The expression of vasculogenic markers for the groups with BMP2/VEGF or VEGF only increased with incubation time, whereas the expression for those groups without BMP2 or VEGF did not change significantly. After 10 days of incubation, the patterned BMP2-P2SPCP-NP/VEGF-NG group (27 in FIGS. 11A-11G) had the highest mRNA expression of vasculogenic markers vWF, VEGFR, VE-cadherin, and CD31, as well as the highest CD31 protein expression followed by the patterned BMP2/VEGF (28 in FIGS. 11A-11G), unpatterned BMP2-P2SPCP-NP+VEGF-NG (26 in FIGS. 11A-11G), and patterned VEGF-NG (32 in FIGS. 11A-11G) groups. For example, the normalized CD31 mRNA expressions (FIG. 11E) of the patterned BMP2-P2SPCP-NP/VEGF-NG, patterned BMP2/VEGF, unpatterned BMP2-P2SPCP-NP+VEGF-NG, and patterned VEGF-NG groups were 100, 68, 60, and 28, respectively, and the normalized CD31 protein expressions of those groups were 1.0, 0.96, 0.9, and 0.75. Similar to the osteogenic markers in FIGS. 9A-9F, the expression of vasculogenic markers for the patterned VEGF-NG group was significantly less than the patterned BMP2-P2SPCP-NP/VEGF-NG, patterned BMP2/VEG, and unpatterned BMP2-P2SPCP-NP+VEGF-NG groups. The fluorescent images for CD31 immunostaining of the patterned BMP2-P2SPCP-NP/VEGF-NG, BMP2/VEGF, and the VEGF-NG groups are shown in FIG. 12. FIG. 12 displays immunofluorescent images of CD31 protein (white) around one of the channels of the cellular constructs for patterned BMP2-P2SPCP-NP/VEGF-NG (left), patterned BMP2/VEGF (center), and patterned BMP2-P2SPCP-NP (right) groups after 21 days of incubation. The top and bottom rows show the stained images in cross-section and along the length of the channel, respectively. The cell nuclei are counter-stained with DAPI (gray). The scale bar is 500 μm. The images show robust vascularization for the patterned BMP2-P2SPCP-NP/VEGF-NG, as well as for the BMP2/VEGF groups. 

1. A hybrid multifunctional macromer comprising a cleavage site, an assembly site, and a solubility region, wherein the cleavage site comprises a first amino acid sequence, the assembly site comprises a second amino acid sequence, and the solubility region comprises a water-soluble polymer, and wherein each of the cleavage side, the assembly site, and the solubility region are linked by one or more covalent bonds.
 2. The hybrid multifunctional macromer of claim 1, wherein the second amino acid sequence comprises at least one phenylalanine.
 3. The hybrid multifunctional macromer of claim 2, wherein the second amino acid sequence comprises between 2-8 sequentially-linked phenylalanine residues.
 4. The hybrid multifunctional macromer of claim 1, wherein the first amino acid sequence comprises at least 4 amino acid residues, and wherein the first amino acid sequence is cleaved by an enzyme.
 5. The hybrid multifunctional macromer of claim 4, wherein the first amino acid sequence comprises KFTK (lysine-phenylalanine-tyrosine-lysine) and wherein the enzyme comprises plasmin.
 6. The hybrid multifunctional macromer of claim 1, wherein the solubility region comprises polyethylene glycol having a molecular weight between about 1.2 kDa to about 9 kDa.
 7. The hybrid multifunctional macromer of claim 1, further comprising a linker.
 8. The hybrid multifunctional macromer of claim 1, further comprising an endcap.
 9. The hybrid multifunctional macromer of claim 7, wherein the linker comprises a succinimide group.
 10. The hybrid multifunctional macromer of claim 8, the endcap comprises a protein.
 11. The hybrid multifunctional macromer of claim 1, wherein the assembly site is not linked to a peptide backbone included in the hybrid multifunctional macromer.
 12. The hybrid multifunctional macromer of claim 1, further comprising a sequence order defining connectivity between the cleavage site, the assembly site, and the solubility region, wherein the sequence order comprises: a first region including the cleavage site linked to the assembly site, a second region including the solubility region, and a third region including the assembly site linked to the cleavage site, and wherein the first region is linked to the second region and the second region is linked to the third region, and wherein the first region and the third region comprise the same cleavage site and the same assembly site.
 13. The hybrid multifunctional macromer of claim 12, wherein the first region is linked to the second region by a linker, and wherein the second region is linked to the third region by the linker.
 14. The hybrid multifunctional macromer of claim 13, wherein the linker comprises a succinimide group.
 15. The hybrid multifunctional macromer of claim 14, further comprising a protein attached to a terminus of the hybrid multifunctional macromer.
 16. The hybrid multifunctional macromer of claim 1, further comprising at least one spacer.
 17. The hybrid multifunctional macromer of claim 16, wherein the spacer comprises glycine.
 18. The hybrid multifunctional macromer of claim 1, wherein the assembly site comprises an N-acetylated residue.
 19. A method for forming a hybrid multifunctional macromer, the method comprising: Synthesizing a backbone amino acid sequence by linking 4-26 amino acids, the backbone amino acid sequence comprising a cleavage site; Synthesizing an assembly peptide by linking an assembly site to an amino acid side chain included in the backbone amino acid sequence; and Attaching a solubility region to the assembly peptide, wherein the assembly site comprises 2-8 amino acid residues, and wherein the solubility region comprises a water-soluble polymer.
 20. The method of claim 19, wherein synthesizing the backbone amino acid sequence comprises chemically attaching the 4-26 amino acids. 